1. Field of the Invention
The present invention relates to an apparatus and method for controlling the light distribution of a headlamp, and more particularly to an apparatus and method for controlling the light distribution of a headlamp so as to control the light distribution of a headlamp for illuminating an area ahead of a vehicle during running in correspondence with a running state.
2. Description of the Related Art
Conventionally, a vehicle is provided with headlamps for improving the forward visibility of a driver for night driving or the like. In general, a pair of headlamps are respectively disposed on the left and right sides of a front end of the vehicle, and illuminate a relatively wide zone. However, since the headlamps are fixed, there are cases where the driver must continuously view a dark zone which is outside the range of illumination by the headlamps of the vehicle depending on the running state of the vehicle, e.g., when the vehicle makes a turn. Thus, there have been cases where an area which the driver needs to view during the running of a vehicle cannot be illuminated brightly.
To overcome this drawback, a headlamp has been proposed which illuminates an area corresponding to the running direction by changing the optical axis of illumination by the headlamp in correspondence with a steering angle (Japanese Patent Application Publication No. 22299/1980). According to this method, however, although the direction of illumination can be changed, the range of illumination is fixed, so that it is impossible to illuminate the area ahead in a wide range. Accordingly, a headlamp apparatus has been proposed in which the degree of the advancing direction of a vehicle is detected from a steering angle or the like, and the area of light illuminated by the headlamp is enlarged or reduced on the basis of a detected value, thereby guaranteeing an area of illumination by the headlamp with respect to the view position of the driver (Japanese Utility Model Application Laid-Open No. 27938/1990).
However, the position viewed by the driver during driving is not uniformly determined by the running direction of the vehicle or the steering angle of the vehicle. Namely, the driver determines the state of the vehicle such as the running direction and the speed by estimating the position which the vehicle is about to reach, and by viewing the vicinity of that position and estimating its condition. Therefore, if the degree of the advancing direction of the vehicle is detected only from the steering angle or the like, the illumination of the light by the headlamps will lag behind the driver's determination, so that the control of the light distribution ahead of the vehicle lags behind, thereby making it impossible to illuminate an optimum position'which provides the driver with information suited to a view prompting an accurate determination. In addition, when making a turn with such headlamps, since the timing of viewing by the driver always precedes the timing of illumination by the headlamps, the driver inevitably views a position which undergoes a shift from a dark condition due to being not illuminated by the headlamps to a bright condition due to being illuminated by the headlamps. Accordingly, when such a shift takes place continually, the driver may experience an unpleasant sensation.